1. Field of the Invention
This invention relates to a water jet propulsor for a marine vessel and, more particularly, to a water jet propulsor powered an integral canned electric motor.
2. Description of the Prior Art
Water jet propulsors are often used as the main drives for high cruising speed leisure, commercial and naval marine vessels. The basic operating principal of water jet propulsion is similar to that of a screw-type propeller system. The propelling force is generated by adding momentum to the water by accelerating a certain flow of water in an astern direction. Water from under the vessel is fed through an inlet duct to an onboard pump which adds head to the water. This head is then applied to increase the velocity when the water passes through an outlet nozzle into the ambient atmospheric pressure. Steering and reversing forces are generating by deflecting the discharged flow using a flow deflection bucket which is typically hydraulically operated. The water jet system is typically located in the stern of the vessel and is positioned at an elevation which enables it to be self priming when activated and which maximizes propulsion efficiency.
Benefits of water jet propulsion include reduced noise, improved maneuverability, protected propulsion installation and shallow draft. The fuel efficiency of water jet propulsors is often better than with traditional sub-cavitating propellers at speeds above 20 to 25 knots, depending on the type of vessel.
FIG. 1 schematically illustrates a typical water jet installation of the prior art. The prior art water jet propulsion systems require a power source, such as a diesel engine, steam turbine or gas turbine, P to be located near the water jet impeller I. In addition, the power source P must be mechanically coupled to the impeller I by a drive shaft D through gear box and clutch T. Drive shaft D must be located within water flow conduit C, thereby interfering with the flow of water. In addition, seals are required around drive shaft D where it passes through the wall of water flow conduit C. This arrangement limits the flexibility for designing the vessel within which such a system is utilized. With this type of arrangement, most of the propulsion weight must be located in the stem of the vessel and the location of the pump center line is dictated by the size of the propulsion components.
There remains a need for a water jet propulsor that does not require a drive shaft to be located in the water flow conduit and which does not require the seals associated with a drive shaft passing through the walls of the water flow conduit. There also remains a need for a water jet propulsor which can be set at an elevation below the vessel static water line that is most convenient for self priming and propulsion efficiency and which does not require an engine or turbine to be located in close proximity thereto. The water jet propulsor of this invention has met these needs.